Device for conveying sheets

ABSTRACT

A device for conveying sheets through a printing machine which ensures the safe transport of the sheet exactly in the prescribed transport path, at a low material expense. The device for conveying sheets through a printing machine is provided with continuous conveyor belts running over deflection rollers, between which the sheets are held by frictional forces and guided one after the other, whereby to generate the frictional forces, rollers are provided which press the conveyor belts against each other along the conveyance path. The contact surfaces of the conveyor belts with the sheet have a surface coating made of a material with a high coefficient of friction relative to the material of the sheet.

FIELD OF THE INVENTION

[0001] This invention relates to a device for conveying sheets through a printing machine.

BACKGROUND OF THE INVENTION

[0002] In printing machines, sheets of different types, sizes, and characteristics are transported through the areas of the printing machine from sheet supply areas to output containers for the printed material. In the process, the sheets cover considerable transport distances, in the course of which the printing operation takes place. The sheets essentially move by conveyor belts or driven belts, which are tensioned around movable, driven rollers. An essential criterion during the transport of the sheet is a frictionless and error-free delivery while reducing errors due to shifting or slipping of the individual sheets or pages, i.e. the position and orientation of the sheet on the conveyor belt or driven belt. The safe transport of the sheet is especially jeopardized for small sheet formats, especially at the transfer areas between two belt systems, and for directional changes of a sheet path, for example during the transfer from a vertical to a horizontal sheet path. A possibility for safeguarding the transport path of the sheet is guiding the sheet on path distances on the tension rollers that are as long as possible, i.e. increasing the number of the tension rollers in the printer. A second possibility is increasing the coefficients of friction of the surfaces of the conveyor belts and in this way, increasing the certainty of the transport of the sheet.

[0003] The mentioned second possibility is disclosed in the patent WO96/10778, which describes an improved separation coating for use in many elastomer structures, for example, printing rollers and belts. The coating includes a thin, stretched polytetrafluoroethylene skin attached to a substrate, with a permeable surface and an impermeable area that is exposed as a contact surface. This usage of two surfaces on a single thin coating makes available on the one hand, an excellent bonding with the substrate material, e.g. a silicon elastomer layer, and is on the other hand, highly insensitive to wear, and insensitive to chemical influences.

[0004] Disadvantageous in the first possibility, among other things, is the high material and structural component requirement and as a result, a higher maintenance susceptibility. The second possibility is a multiple layer construction, whose manufacture requires many operating steps.

SUMMARY OF THE INVENTION

[0005] The purpose of the invention is to produce a device for conveying sheets through a printing machine, which ensures the safe transport of the sheet exactly in the transport path provided, at a low material expense. According to the invention, a device for conveying sheets through a printing machine is provided, having continuous conveyor belts running over deflection rollers, between which the sheets are held by frictional forces and guided one after the other. To generate the frictional forces, rollers are provided which press the conveyor belts against each other along the conveyance path, whereby the contact surfaces of the conveyor belts with the sheet have a surface coating made of a material with a high coefficient of friction relative to the material of the sheet. In an especially advantageous manner, the surface coating can be made out of silicone.

[0006] In order to clean the contact surfaces of the conveyor belts, to prevent soiling of the sheet and to ensure the coefficients of friction of the contact area, at least one cleaning device is assigned to the conveyor belts. This cleaning device can contain set cleaning rollers. Furthermore, at least one of the rollers that are present, which press the conveyor belts against each other along the conveyor path, can be constructed as a cleaning roller. For savings or to supplement the cleaning device, the surface coating of the contact surfaces has a surface that is anti-soiling. The sheet is held and guided in the center in the conveyor direction, whereby to support the edges that overhang out of the conveyor belts, guide elements are provided, on which the sheet lies horizontal to the floor during conveyance. As guide elements, plates, sliding rails, or traveling belts may be provided. Furthermore, during the horizontal conveyance of sheets, several modules are provided with conveyor belt pairs, whereby each module of the conveyor belt lying above is constructed shorter than the conveyor belt lying below, whereby the number of the rollers allocated to the upper conveyor belt is reduced by one relative to the number of the rollers allocated to the conveyor belt lying below. The deflection rollers of the conveyor belt lying above act as tension rollers and each are arranged between the deflection roller of the conveyor belt lying below and the roller adjacent to the deflection roller of the lower conveyor belt. The surface coating can be constructed only in partial areas of the contact surface of the conveyor belt with the sheet. In this way, a material savings is obtained based on the physical phenomenon that the frictional force is independent of the size of the contact area. Furthermore, the surface coating can be constructed advantageously in a strip shape or in the form of separate islands.

[0007] The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings, in which:

[0009]FIG. 1 is a schematic diagram of two sections of conveyor belts of a printing machine with a sectional surface coating according the invention made of a material with a high coefficient of friction; and

[0010]FIG. 2 is a schematic side view of a paper path in a printing machine with deflection rollers and cleaning rollers.

DETAILED DESCRIPTION OF THE INVENTION

[0011]FIG. 1 shows, in an exemplary manner, a section of a conveyor belt 10 and a section of another conveyor belt 15 of a printing machine. Visible on the conveyor belt 15, a surface coating 20 made of a material with a high coefficient of friction relative to the material of the sheet has been applied in sections to the shaded areas on this side of the conveyor belt 15. The conveyor belt 15 transports, on its upper side, the sheet 5 in the direction of the arrow a. A roller 30 is arranged below the section of the conveyor belt 15. Another continuous conveyor belt 10 is arranged above the section of the conveyor belt 15, and above this, another roller 30 is arranged. The rollers 30 function for the so-called interlacing of the conveyor belts 10 and/or 15.

[0012] Below the upper roller 30, a section of the conveyor belt 10 is shown in FIG. 1. This conveyor belt moves in the direction of the arrow a, i.e. in the same direction as the section of the conveyor belt 15. Both conveyor belts 10, 15 are continuous. On the sheets 5 between the conveyor belt 10 and 15, the force F₂ acts by the pressure force of the lower roller 30 from below and the force F₁ acts by the pressure force of the upper roller 30 from above. In the case presented, the conveyor belts 10, 15 are driven by a motor (not shown) in the directions of the curved arrow b, whereby the lower and upper roller 30 run in opposite directions. The rollers 30 are shown set apart at a distance for clarity in this diagram according to FIG. 1, but in operation, the rollers 30 are arranged adjacent to each other, and press the conveyor belts 10, 15 between them.

[0013] From the description above, it is clear that the sheet 5 between the rollers 30 at the nip, i.e. the respective support surface of a roller, is clamped in a narrow area perpendicular to the transport direction. The rollers 30 are depicted in FIG. 1 as circles in a side view for illustrative purposes, but they have, as usual, approximately a length corresponding to the width of the conveyor belts 10, 15 plus a width indicated as an overhang. In order to ensure the running safety, the rollers 30 are constructed to be crowned; i.e., the circumference of the respective rollers 30 is larger in their middle than on their edge. By the rotation of the rollers 30 and the pressure forces F₁, F₂, the conveyor belts 10, 15 with the sheet 5 are moved in the direction indicated by the straight directional arrow a. The sheet 5 is held essentially by frictional forces on the conveyor belts 10, 15 and secured from slipping on the conveyor belts 10, 15. For this purpose, sections of a surface coating 20 are applied onto the conveyor belts 10, 15. In FIG. 1, these are shown by strips running along the conveyor belts 10, 15. In the conveyor belt 15, the surface coating 20 is located, as shown in FIG. 1, on its upper side, on which the sheet 5 lies.

[0014] In the conveyor belt 10, the surface coating [not shown] is located, in this diagram according to FIG. 1, on the underside that faces the sheet 5. The material with the high coefficient of friction relative to the material of the sheet 5 is in this case silicone, an organic compound of silicon with oxygen or carbon. In laboratory tests, it was discovered that silicone is especially suitable as a surface coating for conveyor belts 10, 15. A few properties in relation to the invention are the flexibility, extensibility, and gripping capacity.

[0015] In operation, the sheet 5 lies exclusively on the surface coating 20 made of silicone. FIG. 2 shows in a schematic diagram essential parts of the device for conveying sheets 5 through a printing machine with an arrangement of rollers 30 and deflection rollers 35. A continuous conveyor belt 10 is allocated to the upper rollers 30 and deflection rollers 35, and a continuous conveyor belt 15 is allocated to the lower rollers 30 and deflection rollers 35. The two deflection rollers 35 per respective conveyor belt 10, 15 are each a roller with motor drive for moving the conveyor belts 10, 15 and a tension roller set opposite it. As can be seen, the conveyor belt 10 is tensioned around the upper roller 30 and deflection rollers 35 and the conveyor belt 15 is tensioned around the lower rollers 30 and deflection rollers 35, and these move in the directions indicated by the directional arrows. The surface coating 20 made of a material with a high coefficient of friction relative to the material of the sheet 5 and the sheet 5 are not shown in FIG. 2.

[0016] The conveyor belts 10, 15 are each moved in a circular progression around the deflection rollers 35 acting on them by a drive of one of these deflection rollers 35. The rollers 30 function for the so-called interlacing of the conveyor belts 10, 15 and exert the forces F₁ and F₂ on the conveyor belts 10 and/or 15. The frictional forces are effective between the conveyor belts 10, 15 and the sheet 5 so that the sheet 5 resting on the conveyor belts 10, 15 is moved corresponding to the conveyor belts 10, 15. It is desired that the frictional forces are as large as possible so that a slipping of the sheet 5 can be effectively prevented and the sheet 5 runs through the transport path in an error-free manner, i.e. in correct orientation and position.

[0017] To clean the conveyor belts 10, 15 and especially the surface coating 20 of soiling, set cleaning rollers 40 are provided on the conveyor belts 10, 15. In FIG. 2, one cleaning roller 40 is located above and one below the rollers 30 and deflection rollers 35 with the conveyor belts 10, 15. The cleaning rollers 40 can have their own drive, but are preferably driven by the movement of the conveyor belts 10, 15. With the help of the cleaning rollers 40, the surface coating 20 is cleaned during each revolution and its coefficient of friction is maintained. As an alternative, the rollers 30 can be constructed as cleaning rollers. The number of rollers 30 is reduced in the process in comparison to similar devices for conveying sheets 5, since by the increased coefficients of friction between the sheet 5 and the conveyor belts 10, 15, a constant mechanical pressure by the rollers 30 is not necessary to ensure the safe transport in an error-free orientation without slipping or shifting of the sheet 5.

[0018] The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 

What is claimed is:
 1. Device for conveying sheets (5) through a printing machine, consisting of continuous conveyor belts (10, 15) running over deflection rollers (35), between which the sheets (5) are held by frictional forces and guided one after the other, whereby to generate the frictional forces, rollers (30) are provided which press the conveyor belts (10, 15) against each other along the conveyance path, characterized in that the contact surfaces of the conveyor belts (10, 15) with the sheet (5) have a surface coating (20) made of a material with a high coefficient of friction relative to the material of the sheet (5).
 2. Device according to claim 1, characterized in that the surface coating (20) is made out of silicone.
 3. Device according to claim 1, characterized in that the material of the surface coating (20) has a high extensibility.
 4. Device according to claim 1, characterized in that to clean the contact surfaces, at least one cleaning device is allocated to the conveyor belts (10, 15).
 5. Device according to claim 4, characterized in that as a cleaning device, set cleaning rollers (40) are provided on the conveyor belts (10, 15).
 6. Device according to claim 4, characterized in that at least one roller (30, 35) is provided as a cleaning roller.
 7. Device according to claim 1, characterized in that at least the surface coating (20) of the contact surfaces has an anti-soiling surface.
 8. Device according to claim 1, characterized in that the sheet (5) is held and guided in the center in the conveyance direction, whereby to support the edges overhanging out of the conveyor belts (10, 15), guide elements are provided, on which the sheet (5) lies during the horizontal conveyance.
 9. Device according to claim 8, characterized in that as guide elements, plates, sliding rails or traveling belts are provided.
 10. Device according to claim 1, characterized in that the rollers (30, 35) are each set alternatingly along the conveyance path on the side of the conveyor belts (10, 15) that faces away from the contact surface.
 11. Device according to claim 1, characterized in that during the horizontal conveyance of sheets (5), several modules are provided with conveyor belt pairs, whereby each module of the conveyor belt (10) lying above is constructed shorter than the conveyor belt (15) lying below, whereby the number of the rollers allocated to the upper conveyor belt (10) is reduced by one relative to the number of the rollers allocated to the conveyor belt (15) lying below, and whereby the deflection rollers (35) of the conveyor belt (10) lying above act as tension rollers and each are arranged between the deflection rollers (35) of the conveyor belt (15) lying below and the roller (30) adjacent to the deflection roller (35) of the conveyor belt (15) lying below.
 12. Device according to claim 1, characterized in that the surface coating (20) is constructed in partial areas of the contact surface.
 13. Device according to claim 10, characterized in that the surface coating (20) is constructed in the form of strips or in the form of separate islands. 